The Collaborative International Dictionary of English v.0.48:

Nihilistic \Ni`hil*is"tic\, a.
   Of, pertaining to, or characterized by, nihilism.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nihilistic
    adj 1: of or relating to nihilism

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "nihilistic":
   Cassandra-like, Cassandran, Cassandrian, anarchial, anarchic,
   anarchistic, anarcho-syndicalist, antinomian, baneful, calamitous,
   cataclysmal, cataclysmic, catastrophic, chaotic, consuming,
   consumptive, cynical, deadly, defeatist, demolishing,
   demolitionary, depredatory, desolating, destroying, destructive,
   devastating, disastrous, dismal, disorderly, disorganized, doomful,
   downbeat, extreme, extremist, extremistic, fatal, fateful,
   fratricidal, gloomy, internecine, mildly radical, negative,
   negativistic, nihilist, pessimist, pessimistic, pink, radical,
   ravaging, red, revolutionary, revolutionist, ruining, ruinous,
   self-destructive, subversionary, subversive, suicidal, syndicalist,
   syndicalistic, ultraconservative, ultraist, ultraistic, uncheerful,
   unruly, vandalic, vandalish, vandalistic, wasteful, wasting,
   withering